Halite 1: introduction

To go directly to the unit cell structure, click the link to page 3 below.

Halite, often known as rock salt, is made of sodium chloride. It is colourless but can be found blue, purple, pink, yellow or grey, depending on impurities. Its crystals are often found as perfect cubes. Halite is found in many evaporative deposits where it crystallises out of evaporating brine lakes. It is also found in ancient bedrock all over the world where large extinct salt lakes and seas have evaporated millions of years ago, leaving thick deposits of salt behind.

A fragment of the bulk structure of halite is shown to the left. The chloride ions are green and the sodiums are grey. You will need to rotate the structure to see the sodium ions.

In the structure on the left the relative size of the ions is to scale, and nearest-neighbour ions are virtually in contact. In future pages the ions will not be shown in contact as it obscures the internal structure of the lattice. Rather, they will be scaled to half their atomic radius, ie one eighth of their volume. In any case, the determination of ion size has its problems. What x-ray diffraction determines most accurately are the positions of the nuclei in the lattice.

Go to page 2 to look at the structure in a different representation.

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